Metal gasket

ABSTRACT

A metal gasket is formed by first and second metal base plates. The first metal base plate has a first main bead, and first outer and inner sub-bead sections formed outside and inside the first main bead and projecting outwardly in a direction opposite to the first main bead. The second metal base plate has a second main bead, and second outer and inner sub-bead sections formed outside and inside the second main bead and projecting outwardly in a direction opposite to the second main bead. A distance between the second outer and inner sub-bead sections is greater than that between the first outer and inner sub-bead sections. When the first and second metal base plates are assembled, the second outer and inner sub-bead sections entirely sandwich the first outer and inner sub-bead sections therebetween to substantially abut against each other at side peripheries thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of Ser. No. 10/804,070 filed on Mar.19, 2004.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The invention relates to a metal gasket, such as a cylinder head gasket,to be sandwiched between two members, for example a cylinder head and acylinder block, of an internal combustion engine to seal therearound.

In case joint surfaces of a cylinder head and a cylinder block (cylinderbody) of a vehicle are sealed, combustion gas, cooling water,lubricating oil and the like are sealed by sandwiching a cylinder headgasket therebetween.

To meet demands of reducing weight of an engine and a production cost, acylinder head gasket has been changed to a simple structural cylinderhead gasket formed of one or two metal base plates from a metal laminatetype gasket including a plurality of metal base plates. Therefore, theconstituent plates become one or two, usable materials are limited fromthe aspect of making an engine light, and the kind and number of sealingdevices are also limited, which forces to use relatively simplifiedsealing devices.

Therefore, mainly for a cylinder head gasket, for example as shown inFIG. 13, there has been proposed a gasket 2, wherein a main bead 6A andsub-beads 6B linearly connected to the hem portions of the main bead 6Aare provided to a metal plate 2 so that surface pressures are generatedconcentrically at top portions of the main bead 6A and the sub-beads 6Bto positively seal with large surface pressures (For example, JapanesePatent Publication (KOKAI) No. 11-230355, refer to page 2, FIG. 2).

Also, as a gasket formed of two plates, as shown in FIG. 14, there hasbeen proposed a metal laminate gasket for sealing a port of anintake-exhaust system of an engine, wherein a sectional shape of acircular bead 4 surrounding the port 2 is formed in a wave shape havingtwo continuous mountain-shape portions 4 a, 4 b to project mutually inopposite directions from flat portions of a metal plate 1, and the twometal plates are laminated in such a manner that the top portions of themountain-shape portions 4 a of the circular beads 4 abut against eachother. Therefore, the metal plate 1 is provided with the circular bead 4having two heights of the mountain-shape portions, and the circularbeads 4 of the respective layers are sufficiently subjected to anelastic deformation to thereby effectively prevent leaking of a mediumto be sealed (For example, Japanese Patent Publication (KOKAI) No.2002-54502, refer to page 3, FIG. 2).

However, in the gaskets having such wave-form circular beads, while theyare effective for concentrating the surface pressure or enlarging thecrushed margins, the rigidity is basically determined by the sectionalshape of the beads formed on the plate.

On the other hand, in a cylinder head gasket and the like, even in casethe same gasket is used to seal between the same engine members, thesealing performance required by the kind of a hole to be sealed becomesdifferent. For example, in a hole for a cylinder bore, it is required toseal a combustion gas having a high temperature and a high pressure,while in a liquid hole for circulating cooling water and engine oil, itis required to seal a liquid having a comparatively low temperature andpressure.

Also, from a structural reason of an engine, there are generateddifferent surface pressures in a hole for a cylinder bore surrounded bybolt holes for tightening bolts and a liquid hole located on an outerside so that the pressing forces by the tightening bolts are onlyapplied to one side thereof.

In the metal gasket as described above, in case a bead is simplyprovided, the rigidity of the bead is determined by the shape of thebead, material characteristics of metal of a base plate and a thicknessof the base plate. Therefore, the design freedom is limited, and it isdifficult to provide the optimum sealing performance with respect to therespective holes to be sealed.

Especially, since a high surface pressure is required around the holefor the cylinder bore, in order not to damage the engine members made ofa relatively soft aluminum alloy, it is difficult to use a metal baseplate having a high rigidity. On the other hand, there is also a problemthat a sufficient rigidity can not be obtained with the conventionalshape and arrangement of the bead.

Also, as shown in FIG. 14, in the gasket where the top portions 4 a ofthe mountain-shapes of the wave-forms in a two plate structure abutagainst each other, in case the abutting beads are mis-aligned, since apredetermined compression rigidity of the beads 4 may not be obtained,it is required to carry out the precise alignment of the abutting beads4.

However, in a cylinder head gasket and the like having a fine bead of awidth less than 3 mm, the positioning is actually difficult, so that anadvanced technique is required.

In view of the above, the present invention has been made, and an objectof the invention is to provide a metal gasket of a two plate structureexcellent in sealing ability, such as a cylinder head gasket, whereinsub-beads are respectively provided around main beads disposed torespective metal base plates for sealing a hole to be sealed and thesub-beads abut against each other so that an adequate bead rigidity canbe obtained by constraining the deformation in a radial direction of amain bead of one metal base plate by the sub-bead of the other metalbase plate. Thus, the optimum surface pressure distribution can begenerated around the hole for the cylinder bore or the like andmaintained.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the above objects, a gasket of the invention isformed of a first metal base plate provided with a first main bead and asecond metal base plate provided with a second main bead, wherein thefirst main bead and the second main bead are disposed back to back toproject outwardly around a hole to be sealed. The gasket comprises afirst inner peripheral side sub-bead smaller than the first main beaddisposed on an inner peripheral side of the first main bead; a firstouter peripheral side sub-bead smaller than the first main bead disposedon an outer peripheral side of the first main bead; a second innerperipheral side sub-bead smaller than the second main bead disposed toabut against the first inner peripheral side sub-bead on an innerperipheral side of the second main bead; and a second outer peripheralside sub-bead smaller than the second main bead disposed to abut againstthe first outer peripheral side sub-bead on an outer peripheral side ofthe second main bead.

Incidentally, it is sufficient that the sub-beads abut against eachother under a state where the metal gasket is set. Therefore, theabutment between the sub-beads may include a case where the sub-beads donot abut against each other before they are pressed by a predeterminedpressing force, i.e. in an initial shape without being pressed. Forexample, in the cylinder head gasket, in case the gasket itself is in aninitial state, the sub-beads may not abut against each other. It issufficient that when the gasket is sandwiched between a cylinder headand a cylinder block and tightened by the tightening bolts with apredetermined pressing force, side portions of the sub-beads may abutagainst each other on either inner side or outer side.

According to the structure, diversification and fine adjustment of therigidity of the main beads can be attained by correlating thedeformations of one main bead and the other main bead with abutments ofthe sub-beads, and the accuracy of positioning of the two metal baseplates can be improved.

In other words, the periphery of one main bead, which has a largedeformation quantity in the widthwise direction, can be constrainedthrough abutments of the sub-beads provided on the outer peripheral sideand inner peripheral side of the main beads. Thus, the rigidity can beelevated by constraining a displacement in the widthwise direction ofone main bead.

Moreover, since the degree of the constraint in the radial direction ofone main bead can be adjusted by the shape (here, also including a size)of the other main bead and the material characteristics and platethickness of the metal base plate, a multiple of surface pressures canbe generated through the combination of the two main beads. Thus, a moreadequate sealing line corresponding to a hole to be sealed can be formedto thereby improve the sealing ability of the gasket.

Also, since the sub-beads of one metal base plate and the sub-beads ofthe other metal base plate are disposed to abut against each other intheir side portions, the sub-beads guide each other to positionthemselves. Thus, the two sheets of the metal base plates can be easilyand precisely aligned, and a desired sealing surface pressure can bepositively obtained through combination of the beads.

Then, the mutual abutments between the sub-beads are carried out by atleast one of an abutment between the first inner peripheral sidesub-bead and the second inner peripheral side sub-bead and an abutmentbetween the first outer peripheral side sub-bead and the second outerperipheral side sub-bead, through the abutments of the beads formedinwardly respectively. Or, at least one of the abutment between thefirst inner peripheral side sub-bead and the second inner peripheralside sub-bead and the abutment between the first outer peripheral sidesub-bead and the second outer peripheral side sub-bead is carried outthrough an abutment by fitting one bead into the other bead.

Also, at least one of the first inner peripheral side sub-bead, thesecond inner peripheral side sub-bead, the first outer peripheral sidesub-bead and a second outer peripheral side sub-bead is formed of aplurality of beads. Thus, the constraint in the radial direction can beelevated and the positioning accuracy can be improved.

Then, at least one of the first inner peripheral side sub-bead, thesecond inner peripheral side sub-bead, the first outer peripheral sidesub-bead and the second outer peripheral side sub-bead is intermittentlyprovided in the circumferential direction, so that the strength of thebinding force can be easily adjusted.

In case the sealing is carried out by half beads, in a gasket to attainthe above objects, formed of a first metal base plate and a second metalbase plate, wherein a first main half bead of the first metal base plateand a second main half bead of the second metal base plate are disposedback to back with a projected portion outward, respectively, around ahole to be sealed, a first outer peripheral side sub-bead smaller thanthe first main half bead is provided on an outer peripheral side of thefirst main half bead and a second outer peripheral side sub-bead smallerthan the second main half bead is disposed to abut against a sideportion of the first outer peripheral sub-bead in a side portion thereofon an outer peripheral side of the second main half bead.

Also, in the half bead metal gasket, the abutment between the firstouter peripheral side sub-bead and the second outer peripheral sidesub-bead is structured by the abutment of the side portions of the beadsprojected inward; or the abutment between the first outer peripheralside sub-bead and the second outer peripheral side sub-bead isstructured by fitting one bead into the other bead.

Further, at least one of the first outer peripheral side sub-bead andthe second outer peripheral side sub-bead is discontinuously orintermittently provided in a circumferential direction, so that thestrength of the binding force can be easily adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view with a section showing a cylinderhead gasket of a first embodiment according to the invention;

FIG. 2 is a partial perspective view with a section showing anotherexample of a cylinder head gasket of the first embodiment according tothe invention;

FIG. 3 is a partial sectional view showing a cylinder head gasket of asecond embodiment according to the invention;

FIG. 4 is a partial sectional view showing a cylinder head gasket ofanother example of the second embodiment according to the invention;

FIG. 5 is a partial sectional view showing a cylinder head gasket of athird embodiment according to the invention;

FIG. 6 is a partial sectional view showing a cylinder head gasket ofanother example of the third embodiment according to the invention;

FIG. 7 is a partial perspective view with a section of a cylinder headgasket of a fourth embodiment according to the invention;

FIG. 8 is a partial sectional view showing a cylinder head gasket ofanother example of the fourth embodiment according to the invention;

FIG. 9 is a partial sectional view showing a cylinder head gasket of afifth embodiment according to the invention;

FIG. 10 is a partial sectional view showing a cylinder head gasket ofanother example of the fifth embodiment according to the invention;

FIG. 11 is a partial sectional view showing a cylinder head gasket of asixth embodiment according to the invention;

FIG. 12 is a plan view of a cylinder head gasket of an embodimentaccording to the present invention;

FIG. 13 is a partial sectional view showing a conventional gasket; and

FIG. 14 is a partial sectional view showing a conventional metal gasket.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Next, a cylinder head gasket, as an example, of an embodiment of a metalgasket according to the present invention will be explained withreference to the accompanying drawings.

As shown in FIGS. 1 through 12, metal gaskets 1 and 1A of theembodiments according to the invention are cylinder head gaskets to besandwiched between a cylinder head and a cylinder block (cylinder body)of an engine to seal a combustion gas of high temperature and highpressure from cylinder bores, and a liquid, such as cooling water orcooling oil, flowing through a cooling water path or a cooling oil path.

Incidentally, FIGS. 1 through 12 are schematic views, wherein dimensionsand horizontal to vertical ratios of a plate thickness, a bead, acoating film and the like of the cylinder head gaskets 1, 1A aredifferent from the real measurements, so that sealing portions areexaggerated, which makes them easily understandable.

As shown in FIGS. 1 through 6, FIGS. 7 through 11, and FIG. 12, cylinderhead gaskets 1, 1A according to the present invention include twoplates, i.e. a first metal base plate 10 and a second metal base plate20, formed of an annealed stainless steel, processed stainless steel(spring steel plate), soft iron plate or the like. These metal baseplates 10, 20 are produced in conformity with the shape of an enginemember, such as a cylinder block, and provided with holes 2 for cylinderbores, liquid holes 3 for circulating cooling water and engine oil, boltholes 4 for tightening bolts and the like.

In the present invention, in case a main bead is formed of a full bead,a first main bead 11 of the first metal base plate 10 and a second mainbead 21 of the second metal base plate 20 are disposed back to back,i.e. aligned, around the hole 2 for the cylinder bore to be sealed sothat both beads project outward, respectively.

Also, as shown in FIGS. 1 through 6, in the first metal base plate 10, afirst inner peripheral side sub-bead 12 smaller than the first main bead11 is provided on an inner peripheral side of the first main bead 11,and a first outer peripheral side sub-bead 13 smaller than the firstmain bead 11 is provided on an outer peripheral side of the first mainbead 11, respectively.

Also, in the second metal base plate 20, a second inner peripheral sidesub-bead 22 smaller than the second main bead 21 is provided to abutagainst the first inner peripheral side sub-bead 12 on the innerperipheral side of the second main bead 21, and a second outerperipheral side sub-bead 23 smaller than the second main bead 21 isprovided to abut against the first outer peripheral side sub-bead 13 onthe outer peripheral side of the second main bead 21.

In the first embodiment as shown in FIGS. 1 and 2, the abutment betweenthe first inner peripheral side sub-bead 12 and the second innerperipheral side sub-bead 22 and the abutment between the first outerperipheral side sub-bead 13 and the second outer peripheral sidesub-bead 23 are carried out, respectively, such that the respective sideportions of mutually inward projecting beads abut against each other.

While the first main bead 11 and the second main bead 21 normally havedifferent shapes (including sizes), they may be the same shape. When thefirst main bead 11 and the second main bead 21 have the same shape,since there may be a temperature difference between the first metal baseplate 10 and the second metal base plate 20, the sub-beads 12, 13, 22,23 mainly play a role for mutually positioning the metal base plates 10and 20 though there is deformation constraint of the main beads 11, 21.

In FIG. 1, the first main bead 11 and the second main bead 21 havedifferent shapes, and the sub-beads 12, 13, 22, 23 have a trapezoidalshape. In FIG. 2, the first main bead 11 and the second main bead 21have the same shape, and the sub-beads 12, 13, 22, 23 have a circulararc shape.

Also, in a second embodiment as shown in FIGS. 3 and 4, a first innerperipheral side sub-bead 12 abuts against a second inner peripheral sidesub-bead 22, and a first outer peripheral side sub-bead 13 abuts againsta second outer peripheral side sub-bead 23. The abutments are made suchthat one bead enters the other bead to fit each other.

In FIG. 3, a first main bead 11 and a second main bead 21 and respectivesub-beads 12, 13, 22, 23 are made in a trapezoidal shape. In FIG. 4, thefirst main bead 11 and the second main bead 21 and the respectivesub-beads 12, 13, 22, 23 are made in a circular arc shape.

In a third embodiment of the invention as shown in FIGS. 5 and 6, atleast one of a first inner peripheral side sub-bead 12, a second innerperipheral side sub-bead 22, a first outer peripheral side sub-bead 13and a second outer peripheral side sub-bead 23 is formed of a pluralityof beads.

In FIG. 5, the second outer peripheral side sub-bead is formed of twobeads 23 so that the first outer peripheral side sub-bead 13 issandwiched therebetween. In FIG. 6, further, the first inner peripheralside sub-bead is formed of two beads 12 so that the second innerperipheral side sub-bead 22 is sandwiched therebetween. The number ofthe sub-beads may be two to three, if there is enough room to provide.There is no specific limitation.

In all structures of FIGS. 1 through 6, the sub-beads 12, 13, 22, 23 maybe provided around the whole circumference in the circumferentialdirection, or may be discontinuously or intermittently provided. Withthe length and the position of the sub-beads, the magnitude of theconstraint (strength) in a radial direction of the main bead 11 (or 21)can be finely adjusted.

Incidentally, an example of the dimensions of parts of the gasket willbe shown hereunder. In case a diameter of a hole 2 for a cylinder boreis about 50 mm-90 mm, a thickness of the first metal base plate 10 andthe second metal base plate 20 is 0.10 mm-0.40 mm, respectively; aheight of the trapezoidal beads of the first main bead 11 and the secondmain bead 21 is 0.05 mm-0.30 mm; a bead width (length of the hemportion) is 1.0 mm-5.0 mm; a bead height of the trapezoidal beads of thefirst inner peripheral side sub-bead 12 and the second inner peripheralside sub-bead 22 is 0.01 mm-0.15 mm, and a width of the beads thereof is0.5 mm-3.0 mm; and a height of the trapezoidal beads of the second outerperipheral side sub-bead 13 and the second outer peripheral sidesub-bead 23 is 0.01 mm-0.15 mm, and a bead width thereof is 1.0 mm-3.0mm.

In the present invention, in case the main beads are formed of halfbeads, a first main half bead 11A of the first metal base plate 10 and asecond main half bead 21A of the second metal base plate 20 are disposedback to back, i.e. aligned, to project outwardly around the hole 2 forthe cylinder bore to be sealed.

Also, as shown in FIGS. 7 and 8, the first metal base plate 10 isprovided with a first outer peripheral side sub-bead 13 smaller than thefirst main half bead 11A on an outer peripheral side of the first mainhalf bead 11A, and the second metal base plate 20 is provided with asecond outer peripheral side sub-bead 23 smaller than the second mainhalf bead 21A to abut against the first outer peripheral side sub-bead13 on the outer peripheral side of the second main half bead 21A.

In the fourth embodiment as shown in FIGS. 7 and 8, the abutment betweenthe first outer peripheral side sub-bead 13 and the second outerperipheral side sub-bead 23 is carried out by allowing the respectiveside portions of beads projecting inward to abut against each other.

The first main half bead 11A and the second main half bead 21A arenormally formed in a different shape (including size), but they may havethe same shape. In case they have the same shape, since the temperatureof the first metal base plate 10 may be different from that of thesecond metal base plate 20, the sub-beads 13, 23 mainly play a role formutually positioning the metal base plates 10 and 20 though there isdeformation constraint of the main half beads 11A, 21A.

In FIG. 7, the first main half bead 11A and the second main half bead21A have a different shape, respectively, and the sub-beads 13, 23 havea trapezoidal shape; and in FIG. 8, the first main half bead 11A and thesecond main half bead 21A have the same shape and the sub-beads 13, 23have a circular arc shape.

In a fifth embodiment as shown in FIGS. 9 and 10, the abutment betweenthe first outer peripheral side sub-bead 13 and the second outerperipheral side sub-bead 23 is carried out by fitting one bead into theother bead. In FIG. 9, the respective sub-beads 13, 23 are formed in atrapezoidal shape; and in FIG. 10, the respective sub-beads 13, 23 areformed in a circular arc shape.

In an eighth embodiment as shown in FIG. 11, at least one of the firstouter peripheral side sub-bead 13 and the second outer peripheral sidesub-bead 23 is formed of plural beads. In FIG. 11, the first outerperipheral side sub-bead is formed of two beads 13 to sandwich thesecond outer peripheral side sub-bead 23. The number of the sub-beadsmay be two to three, if there is an enough space, and there is nospecific limitation.

In all structures of FIGS. 7 through 11, the sub-beads 13, 23 may beprovided around the whole circumference in the circumferentialdirection, or may be intermittently provided. By the lengths and thepositions of the sub-beads, the magnitude of the constraint (strength)in a radial direction of the main half-bead 11A (or 21A) can be finelyadjusted.

According to the cylinder head gaskets 1, 1A having the structures asdescribed above, the periphery of one main bead 11 (11A, 21 or 21A),which has a large deformation quantity in the widthwise direction, canbe constrained through abutment of the respective side portions of thesub-beads 12, 13, 22, 23 provided on the outer peripheral side and innerperipheral side of the main beads 11, 21 or the main half beads 11A,21A. Thus, the rigidity of the one main bead 11 (21, 11A, or 21A) can beincreased.

Since the degree of the constraint in the radial direction of one mainbead 11 (11A, 21, or 21A) can be adjusted by the shape of the other mainbead 21 (11, 11A or 21A) and the material characteristics and platethickness of the metal base plate 20 (or 10), a multiple of surfacepressures can be generated through the combination of the main beads 11,21 or the main half beads 11A, 21A.

Also, since the sub-beads 12, 13 of one metal base plate 10 and thesub-beads 22, 23 of the other metal base plate 20 are disposed to abutagainst each other in their side portions, the sub-beads 12, 13, 22, 23guide each other to position themselves. Thus, the two sheets of themetal base plates 10, 20 can be easily and precisely aligned. Byimproving accuracy of the alignment, a desired surface pressure can bepositively obtained to thereby carefully respond to the sealing abilityrequired with respect to the hole 2 for the cylinder bore and improvethe sealing ability.

Since the sealing ability around a liquid hole 3 is not strict to thesealing ability around the hole 2 for the cylinder bore, a desiredsealing ability can be obtained by providing a relatively simple bead31.

Therefore, the cylinder head gasket 1 having the structure as describedabove can respond precisely to the sealing ability required by the hole2 for the cylinder bore and the sealing ability required by the liquidhole 3, respectively. Thus, adequate sealing balances with respect tothe respective portions of the metal gasket 1 or 1A can be attained.

Incidentally, the present invention is not limited to only theseembodiments. The present invention is also applied to metal gaskets forother use, such as an inlet manifold and an exhaust manifold, inaddition to the cylinder head gasket.

As described hereinabove, according to the metal gasket of theinvention, the periphery of one main bead, which has a large deformationquantity in the widthwise direction, can be constrained through abutmentof the sub-beads provided on the outer peripheral side and innerperipheral side of the main beads. Thus, the rigidity of one main beadcan be increased. Since the degree of the constraint in the radialdirection of one main bead can be adjusted by the shape of the othermain bead and the material characteristics and plate thickness of themetal base plate, multiple surface pressures can be generated throughthe combination of the two main beads.

Also, since the sub-beads of one metal base plate and the sub-beads ofthe other metal base plate are disposed to abut against each other intheir side portions, the sub-beads guide each other to positionthemselves. Thus, the two sheets of the metal base plates can be easilyand precisely aligned. By improving accuracy of the alignment, a desiredsurface pressure can be positively obtained.

Therefore, the sealing ability can be improved since the sealingabilities required for the respective holes to be sealed can beadequately dealt and the suitable sealing balances with respect to thevarious portions of the metal gasket can be attained.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

1. A metal gasket having a hole to be sealed, comprising: a first metalbase plate having a first main bead projecting outwardly therefromaround the hole, a first outer sub-bead section smaller than the firstmain bead and provided outside the first main bead, and a first innersub-bead section smaller than the first main bead and provided insidethe first main bead, said first outer and inner sub-bead sectionsprojecting outwardly in a direction opposite to the first main bead, anda second metal base plate laminated with the first metal base plate andhaving a second main bead projecting outwardly therefrom around thehole, a second outer sub-bead section smaller than the second main beadand provided outside the second main bead, and a second inner sub-beadsection smaller than the second main bead and provided inside the secondmain bead, said second outer and inner sub-bead sections projectingoutwardly in a direction opposite to the second main bead, a distancebetween the second outer and inner sub-bead sections being greater thanthat between the first outer and inner sub-bead sections so that whenthe first and second metal base plates are assembled, the second outerand inner sub-bead sections face the first outer and inner sub-beadsections and entirely sandwich the first outer and inner sub-beadsections therebetween to substantially abut against each other at sideperipheries thereof.
 2. A metal gasket according to claim 1, wherein atleast one of the first and second outer sub-bead sections is formedintermittently in a circumferential direction.
 3. A metal gasketaccording to claim 1, wherein said second main bead has a size less thanthat of the first main bead so that when the gasket is compressed, thesecond outer and inner sub-bead sections restrict lateral movements ofthe first outer and inner sub-bead sections.
 4. A metal gasket accordingto claim 1, wherein each of said first and second outer and innersub-bead sections has a trapezoidal shape.
 5. A metal gasket accordingto claim 1, wherein said first and second metal base plates aredifferent in thickness.